Cleanout plug leaking
I have cast iron sewer pipes. Several years ago, when the pipe was clogged, the plumber tried to remove the cleanout plug just inside the cellar wall. About a 3-inch piece of the threads that the plug screws into broke off at the bottom part of the opening. He replaced the cleanout plug with some kind of plug with a metal plate on the outside and a wing nut that expands the rubber (or whatever soft material seals leakage). Now, it's leaking and I fear that Im facing a huge repair bill, unless there is something I can do on my own. Please advise.
Did you try tightening the wingnut?
The line may be clogged with waste water holding in the line putting pressure on the plug. With a bucket under the plug you can carefully loosen the wing nut and see if the leaking increases. Be careful it may want to fly out. If the leaking increases I would call to have the drain cleaned.
If the plug does not have water built up behind it but it is water leaking as it goes by down the waste line, tightening it may stop the leakage.